U.S. patent application number 15/072505 was filed with the patent office on 2016-09-22 for positioner.
This patent application is currently assigned to Azbil Corporation. The applicant listed for this patent is Azbil Corporation. Invention is credited to Kazuhisa INOUE.
Application Number | 20160274593 15/072505 |
Document ID | / |
Family ID | 55661188 |
Filed Date | 2016-09-22 |
United States Patent
Application |
20160274593 |
Kind Code |
A1 |
INOUE; Kazuhisa |
September 22, 2016 |
POSITIONER
Abstract
A first table defines the relationship between the sliding
resistance index .mu.k of a packing gland and the ambient
temperature for each type of the packing gland is provided. A
second table defines control parameters corresponding to hysteresis
levels for each size of the setting/operating device is provided.
By repeating, at regular intervals, the acquisition of the sliding
resistance index .mu.k at present corresponding to the ambient
temperature at present and the type of a packing gland from the
first table and the selection of the control parameter
corresponding to the size of the setting/operating device and the
hysteresis level obtained from the sliding resistance index .mu.k
at present from the second table, the valve opening of the
regulating valve is controlled using the selected control
parameter.
Inventors: |
INOUE; Kazuhisa; (Tokyo,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Azbil Corporation |
Tokyo |
|
JP |
|
|
Assignee: |
Azbil Corporation
Tokyo
JP
|
Family ID: |
55661188 |
Appl. No.: |
15/072505 |
Filed: |
March 17, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G05D 7/0629 20130101;
F15B 19/002 20130101; F16K 37/0083 20130101; F15B 2211/6343
20130101; F15B 5/006 20130101; G05B 2219/41246 20130101 |
International
Class: |
G05D 7/06 20060101
G05D007/06 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 17, 2015 |
JP |
2015-053902 |
Claims
1. A positioner including a controller outputting, as a control
output, an electric signal according to a difference between a
valve opening setting value sent from a higher-level device and an
actual opening value fed back from a regulating valve and an
electric-pneumatic converting portion converting the control output
from the controlling portion to an air pressure and outputting the
air pressure to a setting/operating device of the regulating valve,
the positioner comprising: a characteristic value/ambient
temperature relationship non-transitory storage storing a
relationship between a characteristic value indicating sliding
performance of a valve stem of the regulating valve, the sliding
performance changing depending on an ambient temperature, and the
ambient temperature; a control parameter non-transitory storage
storing correspondence between a level of the characteristic value
and a control parameter used to control a valve opening of the
regulating valve; a temperature sensor measuring the ambient
temperature at present of the regulating valve; a current
characteristic value acquirer acquiring, as the characteristic
value at present, the characteristic value corresponding to the
ambient temperature at present of the regulating valve measured by
the temperature sensor based on the relationship stored in the
characteristic value/ambient temperature relationship
non-transitory storage; and a control parameter selector selecting,
from the control parameter non-transitory storage, the control
parameter corresponding to the level of the characteristic value at
present acquired by the current characteristic value acquirer,
wherein the controller causes the current characteristic value
acquirer to acquire the characteristic value at present and the
control parameter selecting portion to select the control parameter
corresponding to the level of the characteristic value at present
repeatedly at regular intervals and the controller controls the
valve opening of the regulating valve using the selected control
parameter.
2. The positioner according to claim 1, wherein the
setting/operating device of the regulating valve is of a direct
acting type, the characteristic value/ambient temperature
relationship non-transitory storage stores, for each type of a
packing gland used in the regulating valve, a relationship between
a sliding resistance index .mu.k of the packing gland and the
ambient temperature as the characteristic value, the current
characteristic value acquirer acquires, from the relationship
stored in the characteristic value/ambient temperature relationship
non-transitory storage, the sliding resistance index .mu.k
corresponding to the type of the packing gland used in the
regulating valve and the ambient temperature at present of the
regulating valve measured by the temperature sensor as the
characteristic value at present, and the control parameter selector
substitutes the sliding resistance index .mu.k acquired as the
characteristic value at present by the current characteristic value
acquirer into an expression (1) below to obtain a stem motion
resistance F as a sliding resistance of the valve stem of the
regulating valve and selects a control parameter corresponding to a
level of the obtained sliding resistance of the valve stem of the
regulating valve from the control parameter non-transitory storage.
F=.mu.*k*.pi.*D*H*P(N) (1) where .mu. is a friction coefficient, k
is a lateral pressure coefficient, D is a diameter of the valve
stem, H is a height of the packing gland, and P is a fastening
surface pressure of the packing gland, and .mu.k equals .mu.*k.
3. The positioner according to claim 1, wherein the
setting/operating device of the regulating valve is of a rotary
type, the characteristic value/ambient temperature relationship
non-transitory storage stores, for each type of a packing gland
used in the regulating valve, a relationship between a sliding
resistance index .mu.k of the packing gland and the ambient
temperature as the characteristic value, the current characteristic
value acquirer acquires, from the relationship stored in the
characteristic value/ambient temperature non-transitory storage,
the sliding resistance index .mu.k corresponding to the type of the
packing gland used in the regulating valve and the ambient
temperature at present of the regulating valve measured by the
temperature sensor as the characteristic value at present, and the
control parameter selector substitutes the sliding resistance index
.mu.k acquired as the characteristic value at present by the
current characteristic value acquirer into an expression (2) below
to obtain a stem motion resistance F, substitutes the obtained stem
motion resistance F into an expression (3) below to obtain a stem
rotary torque T as a sliding resistance of the valve stem of the
regulating valve, and selects a control parameter corresponding to
a level of the obtained sliding resistance of the valve stem of the
regulating valve from the control parameter non-transitory storage.
F=.mu.*k*.pi.*D*H*P(N) (2) T=(F*D/2)*0.001 (Nm) (3) where .mu. is a
friction coefficient, k is a lateral pressure coefficient, D is a
diameter of the valve stem, H is a height of the packing gland, and
P is a fastening surface pressure of the packing gland, and .mu.k
equals .mu.*k.
4. The positioner according to claim 1, wherein the characteristic
value/ambient temperature relationship non-transitory storage
stores, as a table, a relationship between the characteristic value
indicating the sliding performance of the valve stem of the
regulating valve, the sliding performance changing depending on the
ambient temperature, and the ambient temperature.
5. The positioner according to claim 1, wherein the characteristic
value/ambient temperature relationship non-transitory storage
stores, as an expression, a relationship between the characteristic
value indicating the sliding performance of the valve stem of the
regulating valve, the sliding performance changing depending on the
ambient temperature, and the ambient temperature.
6. The positioner according to claim 1, wherein the control
parameter non-transitory storage stores a correspondence between
the level of the characteristic value and the control parameter
used to control a valve opening of the regulating valve for each
size of the setting/operating device used in the regulating valve
and the control parameter selector selects the control parameter
corresponding to the level of the characteristic value at present
acquired by the current characteristic value acquirer and the size
of the setting/operating device used in the regulating valve from
the control parameter non-transitory storage.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to Japanese Patent
Application No. 2015-053902 filed Mar. 17, 2015. This application
is incorporated herein by reference in its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to a positioner controlling
the opening of a regulating valve.
BACKGROUND
[0003] A conventional positioner is attached to a regulating valve
provided in a pipe through which fluid flows so as to control the
opening of the regulating valve.
[0004] This positioner includes a controlling portion obtaining the
difference between a valve opening setting value sent from a
higher-level device and an actual opening value fed back from the
regulating valve and outputting, as a control output, an electric
signal obtained by applying a predetermined calculation to the
difference, an electric-pneumatic converter converting the control
output from the controlling portion to an air pressure signal, and
a pilot relay amplifying the air pressure signal converted by the
electric-pneumatic converter and outputting the amplified signal to
the setting/operating device of the regulating valve (see Japanese
Unexamined Patent Application Publication S62-28118, for
example).
[0005] FIG. 5 illustrates the structure of the main part of a
conventional positioner. In this drawing, reference numeral 1
indicates a positioner, reference numeral 2 indicates a regulating
valve, and the regulating valve 2 is provided with an opening
sensor 3 detecting the opening (valve opening) of the regulating
valve. The positioner 1 includes a controlling portion 11, an
electric-pneumatic converter (EPM) 12, and a pilot relay 13. The
valve opening of the regulating valve 2 detected by the opening
sensor 3 is fed back to the controlling portion 11 as an actual
opening value .theta.pv.
[0006] In the positioner 1, the controlling portion 11 obtains the
difference between a valve opening setting value .theta.sp from a
higher-level device (not illustrated) and the actual opening value
.theta.pv from the opening sensor 3 and outputs an electric signal
obtained by applying PID control calculation to this difference as
a control output MV.
[0007] The electric-pneumatic converter 12 converts the control
output MV from the controlling portion 11 to an air pressure signal
(nozzle back pressure) Pn. The pilot relay 13 amplifies the air
pressure signal Pn from the electric-pneumatic converter 12 and
outputs the amplified signal to a setting/operating device 2a of
the regulating valve 2 as an air pressure Po. This causes air with
the air pressure Po to flow into the diaphragm chamber of the
setting/operating device 2a to adjust the opening of a valve 2b of
the regulating valve 2.
[0008] In the positioner 1, the electric-pneumatic converter 12 and
the pilot relay 13 constitute an electric-pneumatic converting
portion 14 converting the control output MV from the controlling
portion 11 to the air pressure (output air pressure) Po for the
regulating valve 2. In addition, a supply air pressure
(instrumentation air) Ps from the outside is supplied to the
electric-pneumatic converter 12 and the pilot relay 13.
[0009] FIG. 6 illustrates the main part of the regulating valve 2.
The regulating valve 2 is provided with a valve stem 2d moving up
and down by the air pressure Po from the positioner 1 supplied to a
diaphragm chamber 2c in the setting/operating device 2a and a
packing gland 2f is provided between the outer peripheral surface
of the valve stem 2d and the inner peripheral surface of a stem
insertion hole 2e as illustrated in FIG. 6. The packing gland 2f
includes a plurality of ring-shaped packings provided in close
contact with each other in the shaft direction of the valve stem 2d
so as to prevent fluid from leaking from the gap.
[0010] In the positioner 1, it is necessary to set appropriate
control parameters matching the characteristics of the regulating
valve 2 for the controlling portion 11 to properly control the
opening of the regulating valve 2. For this purpose, before
actually controlling the opening of the regulating valve 2 after
newly installing (or replacing) the regulating valve 2 in the field
or during execution of periodic maintenance, the control parameters
used for the controlling portion 11 are tuned. The tuning of the
control parameters is performed automatically during automatic
setup or the like (see Japanese Patent No. 3511458, for
example).
[0011] In this case, when receiving an automatic tuning
instruction, the controlling portion 11 actually drives the
regulating valve 2 and obtains, as the operation time, the response
time when the valve opening of the regulating valve 2 continuously
shifts from, for example, the 10% position to the 90% position and,
based on the obtained operation time, determines the size of the
setting/operating device 2a with reference to the setting/operating
device size/operation time table defining the correspondence
between the size of the setting/operating device and the operation
time (step S101 illustrated in FIG. 7).
[0012] Then, the controlling portion 11 obtains, as the friction,
the sliding resistance (stem motion resistance) of the valve stem
2d of the regulating valve 2 based on a step response from, for
example, the 40% position to the 60% position of the valve opening
position of the regulating valve 2 (step S102) and determines the
hysteresis level (H/M/L) based on the obtained friction with
reference to a hysteresis level (HYS)/friction table (step
S103).
[0013] Then, the controlling portion 11 selects the corresponding
control parameter with reference to a control parameter table
defining the correspondence among the size of the setting/operating
device, the hysteresis level, and the control parameters based on
the size of the setting/operating device determined in step S101
and the hysteresis level determined in step S103 (step S104) and
sets the selected control parameter as an appropriate control
parameter used to control the opening of the regulating valve 2
(step S105).
SUMMARY
[0014] However, in the conventional positioner, even when an
appropriate control parameter is set according to the size of a
setting/operating device and the hysteresis level using automatic
tuning, since the sliding resistance (friction) of the valve stem
of the regulating valve changes as the ambient temperature of the
regulating valve changes, the control parameter deviates from the
optimum value, overshooting, hunting, and fluctuation of the valve
opening are caused, and fluid control may become unstable.
[0015] In the case of the regulating valve 2 illustrated in FIG. 6,
changes in the sliding resistance (friction) of the valve stem 2d
of the regulating valve 2 are caused mainly by changes in the
shapes of the packing gland 2f and the valve stem 2d due to the
linear expansion coefficients. For example, even when the control
parameter is set to the optimum value by performing the automatic
tuning of the control parameter at an ambient temperature of 20
degrees centigrade, if the ambient temperature changes from -40 to
80 degrees centigrade defined by general product specifications,
the amount of variation in the ambient temperature of the packing
gland 2f is 60 degrees centigrade on the plus and minus sides.
Accordingly, the shapes of the packing gland 2f and the valve stem
2d change due to the linear expansion coefficients and the sliding
resistance (friction) of the valve stem 2d of the regulating valve
2 changes. Accordingly, the control parameter deviates from the
optimum value and overshooting, hunting, and fluctuation of the
valve opening are caused, thereby making fluid control
unstable.
[0016] When the temperature of fluid is high or low, an extension
bonnet 2g is often provided between the setting/operating device 2a
and the valve 2b and the packing gland and the stem portion
(portion A) are structurally separated from a valve portion
(portion B) to form a temperature gradient, and a cold insulating
plate (heat conserving plate) 2h is disposed to minimize the effect
of fluid temperature. Accordingly, the temperatures of most packing
glands and the stem portion (portion A) are almost the same as the
ambient temperature. That is, only the ambient temperature of the
regulating valve 2 needs to be considered. When the ambient
temperature is different from that in the previous tuning, the
turning only needs to be performed again. However, in a field where
daily temperature variation is large, it is difficult to constantly
tune the control parameter to an appropriate value.
[0017] The invention addresses the above problems with an object of
providing a positioner achieving stable fluid control by
suppressing occurrence of overshooting, hunting, and fluctuation of
the valve opening even when the ambient temperature changes
significantly.
[0018] To achieve this object, according to the invention, there is
provided a positioner including a controlling portion outputting,
as a control output, an electric signal according to a difference
between a valve opening setting value sent from a higher-level
device and an actual opening value fed back from a regulating valve
and an electric-pneumatic converting portion converting the control
output from the controlling portion to an air pressure and
outputting the air pressure to a setting/operating device of the
regulating valve, the positioner including a characteristic
value/ambient temperature relationship storing portion storing a
relationship between a characteristic value indicating sliding
performance of a valve stem of the regulating valve, the sliding
performance changing depending on an ambient temperature, and the
ambient temperature, a control parameter storing portion storing
correspondence between a level of the characteristic value and a
control parameter used to control a valve opening of the regulating
valve, a temperature sensor measuring the ambient temperature at
present of the regulating valve, a current characteristic value
acquisition portion acquiring, as the characteristic value at
present, the characteristic value corresponding to the ambient
temperature at present of the regulating valve measured by the
temperature sensor based on the relationship stored in the
characteristic value/ambient temperature relationship storing
portion, and a control parameter selecting portion selecting, from
the control parameter storing portion, the control parameter
corresponding to the level of the characteristic value at present
acquired by the characteristic value acquisition portion, in which
the controlling portion causes the characteristic value acquisition
portion to acquire the characteristic value at present and the
control parameter selecting portion to select the control parameter
corresponding to the level of the characteristic value at present
repeatedly at regular intervals and the controlling portion
controls the valve opening of the regulating valve using the
selected control parameter.
[0019] According to examples of the invention, the ambient
temperature at present of the regulating valve is measured by the
temperature sensor and the characteristic value corresponding to
the ambient temperature at present of the regulating valve measured
by the temperature sensor is acquired as the characteristic value
at present from the relationship stored in the characteristic
value/ambient temperature relationship storing portion. For
example, in the invention, when the characteristic value indicating
the sliding performance of the valve stem of the regulating valve
that changes depending on the ambient temperature is assumed to be
.mu.k (.mu.k=.mu.*k), which is the product of the friction
coefficient .mu. and the lateral pressure coefficient k, then
sliding resistance index .mu.k of the gland packing is acquired as
the characteristic value at present. Then, the control parameter
corresponding to the level (for example, the hysteresis level,
obtained from the sliding resistance index .mu.k of the packing
gland, to which the friction belongs) of the acquired
characteristic value at present is selected from the control
parameter storing portion.
[0020] In the invention, the controlling portion repeats the
acquisition of the characteristic value at present and the
selection of the control parameter corresponding to the level of
the acquired characteristic value at present at regular intervals
and controls the valve opening of the regulating valve using the
selected control parameter. Accordingly, an appropriate control
parameter matching the ambient temperature at present of the
regulating valve is always used and stable fluid control is
achieved.
[0021] Although the ambient temperature at present of the
regulating valve is measured by the temperature sensor in the
invention, the ambient temperature at present of the regulating
valve measured by the temperature sensor may be the temperature
inside the cabinet of the positioner or may be the outside air
temperature. In addition, the characteristic value/ambient
temperature relationship storing portion may store the relationship
between the characteristic value indicating the sliding performance
of the valve stem of the regulating valve, the sliding performance
changing depending on the ambient temperature, and the ambient
temperature as a table or expression. In addition, the
characteristic value/ambient temperature relationship storing
portion may store, for each type of packing glands used for the
regulating valve, the relationship between the sliding resistance
index .mu.k of the packing gland and the ambient temperature as the
characteristic value indicating the sliding performance of the
valve stem of the regulating valve and the control parameter
storing portion may store, for each size of setting/operating
devices used for the regulating valve, the correspondence between
the level of the characteristic value and the control parameter
used to control the opening of the regulating valve.
[0022] According to examples of the invention, since the
acquisition of the characteristic value (characteristic value at
present) indicating the sliding performance of the valve stem of
the regulating valve corresponding to the ambient temperature at
present of the regulating valve and the selection of the control
parameter corresponding to the level of the characteristic value at
present are repeated at regular intervals and the valve opening of
the regulating valve is controlled using the selected control
parameter, by constantly using an appropriate control parameter
matching the ambient temperature at present of the regulating
valve, the occurrence of overshooting, hunting, and fluctuation of
the valve opening is suppressed even when the ambient temperature
significantly changes, thereby achieving stable fluid control.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 illustrates the main part of a positioner according
to an example of the invention.
[0024] FIG. 2 is a functional block diagram illustrating the main
part of a controlling portion of the positioner.
[0025] FIG. 3 illustrates the classification of packing glands used
in a regulating valve.
[0026] FIG. 4 illustrates the sliding resistance index .mu.k that
depends on the types of packings.
[0027] FIG. 5 illustrates the structure of the main part of a
conventional positioner.
[0028] FIG. 6 illustrates the structure of the main part of the
regulating valve.
[0029] FIG. 7 is a flowchart illustrating automatic tuning in a
conventional positioner.
DETAILED DESCRIPTION
[0030] An example of the invention will be described in detail
below with reference to the drawings.
[0031] FIG. 1 illustrates the main part of a positioner according
to the example of the invention. In this drawing, the same
reference numerals as in FIG. 5 indicate the same or similar
components described with reference to FIG. 5 and descriptions are
omitted.
[0032] In the positioner 1 according to the example, a temperature
sensor 15 is provided in the cabinet of the positioner 1 and the
temperature inside the cabinet of the positioner 1 measured by the
temperature sensor 15 is given to a controlling portion 11 as an
ambient temperature TR of the regulating valve 2.
[0033] In the positioner 1, the controlling portion 11 has a
control parameter selecting and setting function F1 for selecting
and setting the optimum control parameter used to control the valve
opening of the regulating valve 2 as a function specific to the
example at regular intervals.
[0034] The positioner 1 in the example is denoted below as 1A to
distinguish it from the conventional positioner 1 (1B) illustrated
in FIG. 5. In addition, the controlling portion 11 in the example
is denoted as 11A to distinguish it from the controlling portion 11
(11B) in the conventional positioner 1B illustrated in FIG. 5. The
controlling portion 11A is configured by hardware including a
processor and memory device and a program achieving various types
of functions in corporation with the hardware.
[0035] FIG. 2 is a functional block diagram illustrating the main
part of the controlling portion 11A. The controlling portion 11A
includes a first table storing portion 16, a second table storing
portion 17, and a control parameter selecting and setting portion
18 to achieve the control parameter selecting and setting function
F1.
[0036] The first table storing portion 16 stores a first table TA
that defines the relationship between the sliding resistance
indexes .mu.k of packing glands and the ambient temperature for
each type of the packing glands by assuming that the characteristic
value in the invention indicating the sliding performance of the
valve stem of the regulating valve that changes depending on the
ambient temperature to be the sliding resistance index .mu.k
(.mu.k=.mu.*k, .mu.: friction coefficient, k: lateral pressure
coefficient) of each of the packing glands.
[0037] The packing glands used for the regulating valve 2 are
classified by application purposes (ultra high temperature
application, high temperature application, and full-time low
temperature application) as illustrated in FIG. 3. Many types of
packing glands having different forms, structural materials, and
application fluids are present and each type has a different
sliding resistance index .mu.k (see FIG. 4).
[0038] In the example, based on experiment and calculation, the
relationship between the sliding resistance indexes .mu.k and the
ambient temperatures for typical packing glands is obtained for
each type of the packing glands (type A (ultra high temperature),
type B (high temperature), and type C (full-time low temperature))
and the obtained relationship is stored as the first table (sliding
resistance index table) TA in the first table storing portion 16.
The relationship between the sliding resistance indexes .mu.k and
the ambient temperatures of the packing glands may be stored as a
temperature characteristic expression.
[0039] The second table storing portion 17 stores the second table
(control parameter table) TB defining the correspondence between
the hysteresis levels (HYS) and the control parameters (KP, TI, TD,
GE, GKP, GTI, and GTD) for each size of a setting/operating device
used in the regulating valve 2 by assuming that the level of the
characteristic value in the invention indicating the sliding
performance of the valve stem of the regulating valve to be the
hysteresis level (HYS). In the example, the hysteresis level (HYS)
is classified into three stages (H, M, and L) and the control
parameters corresponding to these three stages of the hysteresis
level (HYS) are defined.
[0040] The control parameter selecting and setting portion 18
includes a sliding resistance index acquisition portion 18-1, a
friction calculation portion 18-2, a hysteresis level converting
portion 18-3, a parameter selecting portion 18-4, and a parameter
setting portion 18-5. The functions of the individual portions of
the control parameter selecting and setting portion 18 will be
described below together with their operation.
[0041] The operator sets the types of the packing glands used in
the regulating valve 2 for the positioner 1A during the initial
setting or the replacement of the packing gland. The types of the
packing gland set for the positioner 1A are given to the sliding
resistance index acquisition portion 18-1. In addition, the ambient
temperature TR at present of the regulating valve 2 measured by the
temperature sensor 15 is also given to the sliding resistance index
acquisition portion 18-1.
[0042] The sliding resistance index acquisition portion 18-1
receives the type of the packing gland used in the regulating valve
2 and the ambient temperature TR at present of the regulating valve
2 and acquires, as the sliding resistance index .mu.k at present,
the sliding resistance index .mu.k corresponding to the input type
of the packing gland used in the regulating valve 2 and the input
ambient temperature TR at present of the regulating valve 2, from
the first table TA. The sliding resistance index .mu.k at present
acquired by the sliding resistance index acquisition portion 18-1
is sent to the friction calculation portion 18-2.
[0043] The friction calculation portion 18-2 obtains the stem
motion resistance F as the sliding resistance (friction) of the
valve stem 2d of the regulating valve 2 by substituting the sliding
resistance index .mu.k at present from the sliding resistance index
acquisition portion 18-1 into an expression (1) below. A friction F
obtained by the friction calculation portion 18-2 is sent to the
hysteresis level converting portion 18-3.
F=.mu.*k*.pi.*D*H*P(N) (1)
[0044] where D is the diameter (mm) of the valve stem, H is the
height (mm) of the packing gland =, P is the fastening surface
pressure (N/mm.sup.2) of the packing gland, and .mu.k equals
.mu.*k.
[0045] Since the setting/operating device 2a is a direct acting
type setting/operating device in this example, the stem motion
resistance F is obtained as the sliding resistance (friction) of
the valve stem 2d of the regulating valve 2. When the
setting/operating device 2a is a rotary type setting/operating
device, the stem rotary torque T is obtained as the sliding
resistance (friction) of the valve stem 2d of the regulating valve
2 based on an expression (2) below.
T=(F*D/2)*0.001 (Nm) (2)
[0046] The hysteresis level converting portion 18-3 converts the
friction F sent from the friction calculation portion 18-2 to a
hysteresis level (HYS) and sends the converted hysteresis level
(HYS) to the parameter selecting portion 18-4.
[0047] In the example, the hysteresis level (HYS) is classified
into three stages (H, M, and L). The hysteresis level (HYS) to
which the friction F sent from the friction calculation portion
18-2 belongs is selected and the selected hysteresis level (HYS) is
sent from the hysteresis level converting portion 18-3 to the
parameter selecting portion 18-4.
[0048] The size of the setting/operating device 2a used by the
regulating valve 2 is determined during automatic setup. That is,
the size of the setting/operating device is determined using the
setting/operating device size/operation time table based on the
operation time of the setting/operating device 2a. The determined
size of the setting/operating device is given to the parameter
selecting portion 18-4.
[0049] The parameter selecting portion 18-4 receives the size of
the setting/operating device used in the regulating valve 2 and the
hysteresis level (HYS) sent from the hysteresis level converting
portion 18-3 and selects the input control parameter corresponding
to the size of setting/operating device and the input hysteresis
level (HYS) from a second table TB. The control parameter selected
by the parameter selecting portion 18-4 is sent to the parameter
setting portion 18-5.
[0050] When receiving the control parameter from the parameter
selecting portion 18-4, the parameter setting portion 18-5 sets
this control parameter sent from the parameter selecting portion
18-4 as a new control parameter for controlling the opening of the
regulating valve 2 in place of the control parameter used up to
that time.
[0051] The control parameter selecting and setting portion 18
repeats a series of operations performed by the sliding resistance
index acquisition portion 18-1, the friction calculation portion
18-2, the hysteresis level converting portion 18-3, the parameter
selecting portion 18-4, and the parameter setting portion 18-5 at
regular intervals.
[0052] Accordingly, an appropriate control parameter matching the
ambient temperature TR at present of the regulating valve 2 is
always used and, even when the ambient temperature changes
significantly, occurrence of overshooting, hunting, and fluctuation
of the valve opening is suppressed, thereby achieving stable fluid
control.
[0053] In the structure illustrated in FIG. 2, the first table
storing portion 16 corresponds to the characteristic value/ambient
temperature relationship storing portion in the invention, the
second table storing portion 17 corresponds to the control
parameter storing portion, the sliding resistance index acquisition
portion 18-1 corresponds to the current characteristic value
acquisition portion, and the structure including the friction
calculation portion 18-2, the hysteresis level converting portion
18-3, and the parameter selecting portion 18-4 corresponds to the
parameter selecting portion.
[0054] Although the temperature inside the cabinet of the
positioner 1 is measured by the temperature sensor 15 as the
ambient temperature TR of the regulating valve 2 in the above
example, the ambient temperature TR of the regulating valve 2 may
be measured using the temperature sensor 15 provided in the
vicinity of the regulating valve 2 or the outside air temperature
may be used as the ambient temperature TR of the regulating valve
2.
[0055] In addition, when the ambient temperature does not change or
changes slightly in the above example, it is possible to reduce
software loads only by measuring the temperature using the
temperature sensor 15 without acquiring the sliding resistance
index .mu.k by the sliding resistance index acquisition portion
18-1 (that is, without selecting the control parameter by the
control parameter selecting and setting portion 18). Determination
when the ambient temperature does not change or changes slightly
depends on an arbitrary setting.
* * * * *